The primary modern meaning for sally port is a secure, controlled entryway, as at a fortification or a prison. The entrance is usually protected in some way, such as with a fixed wall blocking the door which must be circumvented before entering, but which prevents direct enemy fire from a distance. It may include the use of two doors such as with an airlock.
The word port is ultimately from Latin portus for door. Often the term postern is used synonymously. It can also mean an underground tunnel, or passage (i.e. a secret exit for those besieged).
A sally, ultimately derived from Latin salīre (to jump), or sortie, is a military maneuver, typically during a siege, made by a defending force to harass isolated or vulnerable attackers before retreating back behind their defenses. Sallies are a common way for besieged forces to reduce the strength and preparedness of a besieging army; a sally port is therefore essentially a door in a castle or city wall that allows troops to make sallies without compromising the defensive strength of the fortifications.
Targets for these raids included tools which could be captured and used by the defenders, labor-intensive works such as trenches and mines, and siege engines and siege towers. Sometimes enemy laborers were also targeted. Often, the besiegers' beer and food supplies would be stolen or, if they were too bulky to transport, urinated in.
Modern personnel sally ports are used to control entry into highly protected and restricted military areas, e.g. nuclear weapons storage areas, highly sensitive (and large) conventional weapons storage areas, e.g. small arms, munitions, etc. Sally ports are also used to control entry to highly valuable civilian facilities such as currency or credit card manufacturing sites.
A guard in a protected location (today usually physically remote from the actual sally port) will have control over the middle space between the two doors; the operation of the doors of the sally port; and the movement of all persons, materials and/or vehicles through the sally port. This sally port guard will have the means to check the personnel escorts and/or the credentials of all those persons, materials and vehicles to be passed into the protected space through the first opened door, prior to its opening. He will then monitor the sally transit to ensure that:
Sally ports must be used with caution, and transit through them must be carefully monitored during any emergency or non-routine movements. The greatest safety hazard in use of these passageways is the danger of overcrowding the middle space between the doors. Since either door can only be opened while the other is closed and locked, overcrowding may occur in the middle space when too many persons, vehicles or materials attempt to enter it at once.
Once the middle space is overcrowded, it may be impossible to properly close and lock the first door, thereby also making it impossible to open the second door, which of course is the only way by which people, vehicles or materials can successfully exit the controlled area. Even when the sally port has over-rides installed within the door controls and locking apparatus, the size of the middle space and the physical dimensions and layout of the door openings will act to hamper quick egress of a controlled space through a sally port type opening.
Because of this danger, controlled spaces protected by sally ports usually have multiple sally port openings, safety zones within the controlled space (for internal evacuation w/o leaving the controlled area), and formally written and routinely practiced procedures for the evacuation of persons, vehicles or materials. There is also continuous supervision and monitoring of the total number of persons, vehicles or materials within the controlled space to ensure that the designed evacuation maximum (by whatever evacuation procedure) is never exceeded.
Sally ports are also used to restrict the flow of people to one at a time so that intruders cannot pass into the classified or secure area on a cleared person's coattails.
Military vehicular sally ports are similar to the personnel sally ports but have, of physical necessity, a large middle space to control the incoming/outgoing vehicle and personnel mounted in the vehicle. Mounted personnel are made to stand down, and the vehicles are inspected by guards.
If the person or vehicle in the middle space is found to be unauthorized, the guard can "lock down" both gates, trapping the individual in question until a guard or police response force can neutralize and remove the person and/or vehicle.
A sally port appears on the Coat of Arms of the Republic of Malta
In the modern court building, a sally port secures the prisoners in a holding area or brings them directly from the jail area separating them from the court, with entry through the sally port controlled by the bailiff.
In "supermax" correctional facilities, groups of inmate cells may be connected to central corridors via sally ports. An officer behind protective glass opens the port doors individually after verifying that the person is allowed to pass.
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